librustc: Remove `fail_unless!`
librustc: Implement fast-ffi and use it in various places
rustllvm: Fix RustWrapper.cpp
librustc: Switch the `@`s in types with `~`
librustc: Take primitive types out of the type hash table.
librustc: Remove def_ids from types.
librustc: Optimize metadata::decoder::item_name.
libstd: Micro-optimize vuint_at
rt: Fix scalability problem with big stacks on 32 bit
librustc: Improve inlining behavior.
llvm: Fixes for RustWrapper.
auto merge of #5858 : pcwalton/rust/various-optimizations, r=brson

r? @brson